In the first results of its investigation into the firestorms that erupted across Northern California last October, Cal Fire said Friday that PG&E allegedly failed to remove or trim trees next to power lines that sparked three wildfires in Butte and Nevada counties last fall.

Cal Fire said its investigators found evidence in both counties that PG&E violated state code requiring utilities to maintain adequate clearance between power lines and vegetation.

PG&E said it looked forward to reviewing the findings. “Based on the information we have so far, we believe our overall programs met our state’s high standards,” the company said in a statement.

Cal Fire has not released the results of its investigation into the cause of the massive wildfires that exploded Oct. 8 in Sonoma, Napa, Mendocino and Lake counties. The fires killed 40 people, destroyed almost 6,200 homes and triggered more than $9.5 billion in insured claims in the North Bay.

Friday’s announcement focused on four smaller fires that broke out Oct. 8 and 9 in rural Butte and Nevada counties, where they burned 9,390 acres and destroyed 134 structures. No one was injured or killed.

All four fires were caused by branches or trees that had fallen onto PG&E lines, Cal Fire said. In three of the fires, investigators found evidence the San Francisco utility violated state codes designed to prevent fires by keeping tree limbs clear from power lines. They include:

The Lobo fire in Nevada County, which broke out the night of Oct. 8 and burned 821 acres and destroyed 47 structures.

The McCourtney fire in Nevada County, which started on the evening of Oct. 8 and burned 76 acres and destroyed 13 structures.

The Honey fire in Butte County, which started in the early morning of Oct. 9 and burned 76 acres. No structures were destroyed in the blaze.

Cal Fire found no evidence of violations by PG&E in a fourth wildfire, the La Porte fire, which started in early Oct. 9 in Butte County. It burned 8,417 acres and destroyed 74 structures.

The findings were sent to the district attorney’s offices in Nevada and Butte counties for review as well to the California Public Utilities Commission, which could fine PG&E if it violated agency rules.

In addition, the company faces dozens of lawsuits seeking damages from residents who lost homes in the blazes as well as claims by local governments and insurance companies.

PG&E is lobbying the state Legislature to change state law that permits regulators to hold utilities liable for property damage and attorney fees when their equipment has been found to be the leading cause of a wildfire.

The four fires in Butte and Nevada counties were among more than 170 fires that broke out across Northern California last October, charring more than 245,000 acres. More than 11,000 firefighters from 17 states fought the blazes.

Attorney John Fiske, who represents Sonoma, Napa and Mendocino counties in their litigation against PG&E, said in a statement that he believes the cause disclosed Friday for the four fires will be similar for the North Bay fires.

“The Cal Fire report confirms what we’ve known — that PG&E’s failure to follow the law, and failure to follow basic vegetation management practices, causes devastating wildfires,” Fiske said. “These utility caused wildfires are preventable when multibillion-dollar investor-owned utilities are managed responsibly. This report may be the first step towards rebuilding the communities affected by those fires.”

PG&E said the October fires occurred following “an unprecedented confluence of weather-related conditions,” including a drought that killed millions of trees, followed by a record-setting wet winter that spurred the growth of vegetation and a hot summer that turned it into an tinder box that exploded during high winds.

The utility said it prunes or removes approximately 1.4 million trees annually and inspects every overhead electric transmission and distribution line each year.